Re: [PATCH v2 1/7] mm,memory_hotplug: Allocate memmap from the added memory range

[David Hildenbrand]

> > > +		(*online_page_callback)(pfn_to_page(pfn), pageblock_order);
> > > +		pfn += 1 << pageblock_order;
> >
> > pfn += pageblock_nr_pages;
> >
> > Can you add a comment why we can be sure that we are off by  a single pageblock? What about s390x where a MAX_ORDER_NR_PAGES == 4 * pageblock_nr_pages?
> >
> > Would it make thing simpler to just do a
> >
> > while (!IS_ALIGNED(pfn, MAX_ORDER_NR_PAGES)) {
> > 	(*online_page_callback)(pfn_to_page(pfn), 0);
> > 	pfn++;
> > }
>
> Honestly, I did not spend much time thinking on other platforms other
> than arm64/x86_64.
> But I think that that would be the universal solution as we do not make
> any assumptions.
>
> I will replace it.


I think you can safely go with

while (!IS_ALIGNED(pfn, MAX_ORDER_NR_PAGES)) {
	(*online_page_callback)(pfn_to_page(pfn), pageblock_order);
	pfn += pageblock_nr_pages;
}

and maybe add before the loop

VM_BUG_ON(!IS_ALIGNED(pfn, pageblock_nr_pages));

as help for the reader that this always holds.

--
Thanks,

David / dhildenb